(Updated with Apple response) A vulnerability in iOS 6.1 allows people to bypass the iPhone's lockscreen without entering a passcode, reports say. To accomplish the hack, a person has to go to the Emergency Call screen, begin to power off, but then cancel and make a call which should also be cancelled. The phone next has to be put into standby, woken up, and then swiped; the bypass is finally possible by tapping the Emergency Call button after holding down the power button for three to four seconds. The home button has to be hit right away to prevent the phone from shutting off, and users are still blocked from email, messaging, and browsing.

The trick does let people view and edit contacts though, as well as listen to voicemail messages, or browse photos through trying to add one to a contact. The bug has been verified by a number of outlets, including The Verge and AppleInsider.
iOS has had problems with lockscreen bypasses in the past, namely with iOS 4.1. So far iOS 6.1 has proven a problematic release; people have reported trouble with Exchange support, battery life, and overheating, and in the case of the iPhone 4S, issues with connecting to 3G data. Apple did issue iOS 6.1.1 to solve some of these problems, but only to 4S owners.
Update: Apple spokeswoman Trudy Muller states that the company is aware of the problem, and is planning to fix it in a later update.